NAME

SYNOPSIS

DESCRIPTION

File locks are not part of persistent file system state. Lock state is
thus lost when a host reboots.
Network file systems must also detect when lock state is lost because a
remote host has rebooted. After an NFS client reboots, an NFS server
must release all file locks held by applications that were running on
that client. After a server reboots, a client must remind the server
of file locks held by applications running on that client.
For NFS version 2 [RFC1094] and NFS version 3 [RFC1813], the NetworkStatusMonitor protocol (or NSM for short) is used to notify NFS peers
of reboots. On Linux, two separate user-space components constitute
the NSM service:
rpc.statd
A daemon that listens for reboot notifications from other hosts,
and manages the list of hosts to be notified when the local
system reboots
sm-notify
A helper program that notifies NFS peers after the local system
reboots
The local NFS lock manager alerts its local rpc.statd of each remote
peer that should be monitored. When the local system reboots, the sm-notify command notifies the NSM service on monitored peers of the
reboot. When a remote reboots, that peer notifies the local rpc.statd,
which in turn passes the reboot notification back to the local NFS lock
manager.

NSMOPERATIONINDETAIL

The first file locking interaction between an NFS client and server
causes the NFS lock managers on both peers to contact their local NSM
service to store information about the opposite peer. On Linux, the
local lock manager contacts rpc.statd.
rpc.statd records information about each monitored NFS peer on
persistent storage. This information describes how to contact a remote
peer in case the local system reboots, how to recognize which monitored
peer is reporting a reboot, and how to notify the local lock manager
when a monitored peer indicates it has rebooted.
An NFS client sends a hostname, known as the client’s caller_name, in
each file lock request. An NFS server can use this hostname to send
asynchronous GRANT calls to a client, or to notify the client it has
rebooted.
The Linux NFS server can provide the client’s caller_name or the
client’s network address to rpc.statd. For the purposes of the NSM
protocol, this name or address is known as the monitored peer’s
mon_name. In addition, the local lock manager tells rpc.statd what it
thinks its own hostname is. For the purposes of the NSM protocol, this
hostname is known as my_name.
There is no equivalent interaction between an NFS server and a client
to inform the client of the server’s caller_name. Therefore NFS
clients do not actually know what mon_name an NFS server might use in
an SM_NOTIFY request. The Linux NFS client uses the server hostname
from the mount command to identify rebooting NFS servers.
Rebootnotification
When the local system reboots, the sm-notify command reads the list of
monitored peers from persistent storage and sends an SM_NOTIFY request
to the NSM service on each listed remote peer. It uses the mon_name
string as the destination. To identify which host has rebooted, the
sm-notify command normally sends the results of gethostname(3) as the
my_name string. The remote rpc.statd matches incoming SM_NOTIFY
requests using this string, or the caller’s network address, to one or
more peers on its own monitor list.
If rpc.statd does not find a peer on its monitor list that matches an
incoming SM_NOTIFY request, the notification is not forwarded to the
local lock manager. In addition, each peer has its own NSMstatenumber, a 32-bit integer that is bumped after each reboot by the sm-notify command. rpc.statd uses this number to distinguish between
actual reboots and replayed notifications.
Part of NFS lock recovery is rediscovering which peers need to be
monitored again. The sm-notify command clears the monitor list on
persistent storage after each reboot.

OPTIONS

-d, --no-syslog
Causes rpc.statd to write log messages on stderr instead of to
the system log, if the -F option was also specified.
-F, --foreground
Keeps rpc.statd attached to its controlling terminal so that NSM
operation can be monitored directly or run under a debugger. If
this option is not specified, rpc.statd backgrounds itself soon
after it starts.
-h, -?, --help
Causes rpc.statd to display usage information on stderr and then
exit.
-H,--ha-calloutprog
Specifies a high availability callout program. If this option
is not specified, no callouts are performed. See the High-availabilitycallouts section below for details.
-L, --no-notify
Prevents rpc.statd from running the sm-notify command when it
starts up, preserving the existing NSM state number and monitor
list.
Note: the sm-notify command contains a check to ensure it runs
only once after each system reboot. This prevents spurious
reboot notification if rpc.statd restarts without the -L option.
-n,--nameipaddr|hostname
Specifies the bind address used for RPC listener sockets. The
ipaddr form can be expressed as either an IPv4 or an IPv6
presentation address. If this option is not specified,
rpc.statd uses a wildcard address as the transport bind address.
This string is also passed to the sm-notify command to be used
as the source address from which to send reboot notification
requests. See sm-notify(8) for details.
-N Causes rpc.statd to run the sm-notify command, and then exit.
Since the sm-notify command can also be run directly, this
option is deprecated.
-o,--outgoing-portport
Specifies the source port number the sm-notify command should
use when sending reboot notifications. See sm-notify(8) for
details.
-p,--portport
Specifies the port number used for RPC listener sockets. If
this option is not specified, rpc.statd chooses a random
ephemeral port for each listener socket.
This option can be used to fix the port value of its listeners
when SM_NOTIFY requests must traverse a firewall between clients
and servers.
-P,--state-directory-pathpathname
Specifies the pathname of the parent directory where NSM state
information resides. If this option is not specified, rpc.statd
uses /var/lib/nfs by default.
After starting, rpc.statd attempts to set its effective UID and
GID to the owner and group of this directory.
-v, -V, --version
Causes rpc.statd to display version information on stderr and
then exit.

SECURITY

The rpc.statd daemon must be started as root to acquire privileges
needed to create sockets with privileged source ports, and to access
the state information database. Because rpc.statd maintains a long-
running network service, however, it drops root privileges as soon as
it starts up to reduce the risk of a privilege escalation attack.
During normal operation, the effective user ID it chooses is the owner
of the state directory. This allows it to continue to access files in
that directory after it has dropped its root privileges. To control
which user ID rpc.statd chooses, simply use chown(1) to set the owner
of the state directory.
You can also protect your rpc.statd listeners using the tcp_wrapper
library or iptables(8). To use the tcp_wrapper library, add the
hostnames of peers that should be allowed access to /etc/hosts.allow.
Use the daemon name statd even if the rpc.statd binary has a different
filename.
For further information see the tcpd(8) and hosts_access(5) man pages.

ADDITIONALNOTES

Lock recovery after a reboot is critical to maintaining data integrity
and preventing unnecessary application hangs.
To help rpc.statd match SM_NOTIFY requests to NLM requests, a number of
best practices should be observed, including:
The UTS nodename of your systems should match the DNS names that
NFS peers use to contact them
The UTS nodenames of your systems should always be fully
qualified domain names
The forward and reverse DNS mapping of the UTS nodenames should
be consistent
The hostname the client uses to mount the server should match
the server’s mon_name in SM_NOTIFY requests it sends
The use of network addresses as a mon_name or a my_name string
should be avoided when interoperating with non-Linux NFS
implementations.
Unmounting an NFS file system does not necessarily stop either the NFS
client or server from monitoring each other. Both may continue
monitoring each other for a time in case subsequent NFS traffic between
the two results in fresh mounts and additional file locking.
On Linux, if the lockd kernel module is unloaded during normal
operation, all remote NFS peers are unmonitored. This can happen on an
NFS client, for example, if an automounter removes all NFS mount points
due to inactivity.
High-availabilitycalloutsrpc.statd can exec a special callout program during processing of
successful SM_MON, SM_UNMON, and SM_UNMON_ALL requests. Such a program
may be used in High Availability NFS (HA-NFS) environments to track
lock state that may need to be migrated after a system reboot.
The name of the callout program is specified with the -H option. The
program is run with 3 arguments: The first is either add-client or del-client depending on the reason for the callout. The second is the
mon_name of the monitored peer. The third is the caller_name of the
requesting lock manager.
IPv6andTI-RPCsupport
TI-RPC is a pre-requisite for supporting NFS on IPv6. If TI-RPC
support is built into rpc.statd, it attempts to start listeners on
network transports marked /etc/netconfig. As long as at least one
network transport listener starts successfully, rpc.statd will operate.